So, what exactly is NATO's purpose? That question hangs like a cloud of existential angst over the Atlantic Alliance's 60th birthday celebration this weekend. The festivities, which will span the Franco-German border, are suffused with the symbolism of a Cold War that brought NATO into being but whose end left the Alliance with no clear mission or identity. Hence the title of this anniversary summit: "NATO in 2020: What Lies Ahead?"

Today's world is vastly changed from that of 1949, when the U.S. and Europe agreed to pool their military resources and combine to resist any westward encroachment by the Soviet Union. Most of today's leaders of NATO member states were not yet born when the Alliance was forged, and almost two decades after the Soviet Union's collapse, military analysts see the Alliance as being mired in an identity crisis. "It's entirely unclear what NATO's reason for existence is after 1989 [the year the Berlin Wall came down]," says Tarak Barkawi, a senior lecturer in international security at Cambridge University's Center for International Studies. (See pictures of NATO's peacekeeping mission in Kosovo.)

Originally conceived simply as a mutual-defense pact among its members, the Alliance began to adopt a more expansive role during the 1990s, tackling the crises of Bosnia and Herzegovina and Kosovo as Yugoslavia collapsed. Today, NATO forces continue to provide the bulk of peacekeeping troops in those countries.

But only once in NATO's history has it invoked Article 5 of its charter, which deems an attack on any one member state an attack on all and obliges all to respond collectively. That was the day after the 9/11 attacks in the U.S., and it laid the groundwork for NATO's current role in Afghanistan. That's the prime focus of the summit media packages, which include hours of footage of NATO forces in Afghan villages, highlighting projects such as health clinics and schools. "I didn't even know the [Afghan] provinces when I came to NATO five years ago," joked outgoing Secretary General Jaap de Hoop Scheffer at a NATO Youth Forum in Strasbourg, France, on Thursday. "Now I think I know them all."

Afghanistan, however, is far away from the North Atlantic region where NATO pledged to keep the peace, and the Alliance is staking its credibility on a war in which Western forces are struggling. "The Taliban does not accept defeat, so how can you win?" says Karl-Heinz Kamp, director of the research division of the NATO Defense College in Rome, which trains all ranking NATO officials and diplomats. "NATO might not be able to lose or win in a classic military way," he adds.

And apropos of credibility, although NATO commands the International Security Assistance Force mission in Afghanistan, many of the troop contingents are sent with caveats that prevent them from being used in combat. Instead, the bulk of the fighting there has been done by the 36,000 American soldiers  and small contingents of British, Canadian and Dutch troops.

U.S. President Barack Obama recently decided to send 17,000 more soldiers to Afghanistan in the hopes of stopping the Taliban's momentum. But the limited reinforcements made available by the Europeans  and the restriction to noncombat roles in order to win the consent of Europe's mostly antiwar electorates  have raised questions about the purpose of the Alliance. "NATO lost its credibility when it refused to commit the resources needed," says Barkawi. After several appeals by then President George W. Bush for more combat troops from Europe failed to secure significant reinforcements, the Obama Administration has made clear that it won't even bother to ask in Strasbourg this weekend. In Europe, says De Hoop Scheffer, a former Dutch politician, "fighting is not very popular."

Yet NATO doesn't have much more going on besides the bitter, remote war to which its member nations are reluctant to commit blood and treasure. During the 1990s, the Alliance began expanding, inducting nine new members from Eastern Europe's former Soviet territories and satellites that sought protection from Russian power. But that program seemed to hit a wall last August, when Georgia fought a five-day war against Russia for control of South Ossetia. Georgia, whose bid to join the Alliance had been strongly backed by the U.S., was viewed by many Western officials as having provoked a senseless fight that would have obliged NATO to get involved had Georgia been a full member. Last summer's confrontation put Georgia's prospective membership in the deep freeze, as well as that of Ukraine, whose accession to NATO would also be taken by Moscow as provocation. Moreover, NATO's passivity in the face of Russia's pummeling of Georgia would have left member nations along Russia's western frontier wondering what extent of support they could rely on from NATO allies in the event of a confrontation with Moscow.

Although the Alliance formally inducts Albania and Croatia this weekend, the question mark over its purpose and future persists. One consolation: while NATO gropes for a raison d'être, so too do some of its detractors  Europe's feisty antiwar organizations. Six years after millions of Europeans took to the streets to demonstrate against U.S. plans to invade Iraq, the protest of the latest NATO summit is a sorry affair by comparison. Some 1,000 activists are camped in tents on the edge of Strasbourg in the so-called anti-NATO village, vowing to disrupt this weekend's summit. Several hundred of them, their faces hidden behind black ski masks, gathered in the camp on Thursday afternoon under a warm sun, preparing to storm into Strasbourg. Several stuffed empty glass bottles under black sweatshirts before setting off through the suburbs, chanting "Solidarity! Solidarity!"

In truth, the peace movement has seen some of its fire snuffed out by the departure of President Bush from the White House. After years in which the U.S. President was routinely burned in effigy at such events, there were no anti-American slogans or defaced portraits of Obama visible in the protest camp on Thursday. Asked if Obama had complicated the activists' message, Roel Stynen, 28, a Belgian philosophy graduate from the organization Vredesactie (Peace Action), answered, "Yes, definitely. The Belgian government has said as much, that it was a lot easier to refuse requests from Bush." The demonstrators hurled their bottles at riot police in central Strasbourg on Thursday afternoon before being dispersed by tear gas. Some things have not changed. While activists may take comfort in the arrival of the usual suspects to protest at the NATO summit, it won't help delegates find a sense of common purpose for the next decade.